Precipitation amounts over the past 24 hours varied from trace amounts in the middle of the basin to over an inch in some locations in far western areas and in some parts of the DC metro area. Given the locations of the heaviest rainfall amounts, only a modest increase in flows at the USGS gage at Point of Rocks has occurred at this time. Flows remain below the threshold for daily monitoring. Over the next three days, the Middle Atlantic River Forecast Center predicts widespread rainfall ranging from half an inch to two inches, with higher amounts expected in northeastern areas of the basin.
Recent basin-wide average precipitation (above Little Falls):
(based on CO-OP's Low Flow Forecast System analysis of Middle Atlantic River Forecast Center (MARFC) gridded multisensor precipitation estimates)
Yesterday's area-weighted average basin precipitation: 0.27 (inches)
Past 3-day cumulative area-weighted average basin precipitation: 0.35 (inches)
Past 7-day cumulative area-weighted average basin precipitation: 0.54 (inches)
Daily flows:
Little Falls gage flow 2023-08-06: 847 MGD (1310 cfs)
Little Falls gage flow 2023-08-07: 1622 MGD (est., based on recently available real-time data) (2510 cfs)
Note: Gage flow at Little Falls is measured after water supply withdrawals.
Point of Rocks flow 2023-08-06: 1053 MGD (1630 cfs)
Point of Rocks flow 2023-08-07: 1073 MGD (est., based on recently available real-time data) (1660 cfs)
Yesterday's Washington metropolitan area Potomac River withdrawals and discharges (2023-08-06):
Fairfax Water Corbalis withdrawal (Potomac): 112 MGD
WSSC Water Potomac withdrawal: 135 MGD
Washington Aqueduct withdrawal: 138 MGD
Loudoun Water withdrawal: 13 MGD
Loudoun Water Broad Run discharge: 6 MGD
Total Potomac withdrawal: 398 MGD
Total net Potomac withdrawal: 392 MGD
Loudoun Water Potomac River (PR) flow values for drought operations protocol (based on yesterday's flows):
QPR: 1630 cfs
QPR, obs: 1630 cfs
QPR, WS: 0 cfs
Note to Loudoun Water: See NWS ensemble flow forecasts (HEFS, GEFS, NAEFS) for Point of Rocks flow for the next 7 days – see https://www.weather.gov/erh/mmefs_marfc?id=PORM2&model=NAEFS.
Note: Potomac River flow at Point of Rocks has dropped below the low-flow threshold of 2,000 cfs. When this occurs, per the Water Supply Coordination Agreement of 1982, CO-OP begins daily monitoring and reporting of Potomac flows and withdrawals on behalf of the CO-OP suppliers, Fairfax Water, Washington Aqueduct, and WSSC Water. Suppliers can review data at CO-OP's Data Portal at www.icprbcoop.org. Reports formatted in approved templates should be submitted by email to coop@icprb.org by 8:00 am for automated processing. Published monitoring reports are at http://icprbcoop.org/products/monitoring-reports.